Normal sinus rhythm of the heart begins with the sinoatrial node (or “SA node”) generating an electrical impulse. The impulse usually propagates uniformly across the right and left atria and the atrial septum to the atrioventricular node (or “AV node”). This propagation causes the atria to contract in an organized manner to transport blood from the atria to the ventricles, and to provide timed stimulation of the ventricles. The AV node regulates the propagation delay to the atrioventricular bundle (or “HIS” bundle). This coordination of the electrical activity of the heart causes atrial systole during ventricular diastole. This, in turn, improves the mechanical function of the heart. Atrial fibrillation occurs when anatomical obstacles in the heart disrupt the normally uniform propagation of electrical impulses in the atria. These anatomical obstacles (called “conduction blocks”) can cause the electrical impulse to degenerate into several circular wavelets that circulate about the obstacles. These wavelets, called “reentry circuits,” disrupt the normally uniform activation of the left and right atria.
Because of a loss of atrioventricular synchrony, people who suffer from atrial fibrillation and flutter also suffer the consequences of impaired hemodynamics and loss of cardiac efficiency. They are also at greater risk of stroke and other thromboembolic complications because of loss of effective contraction and atrial stasis.
One surgical method of treating atrial fibrillation by interrupting pathways for reentry circuits is the so-called “maze procedure,” which relies on a prescribed pattern of incisions to anatomically create a convoluted path, or maze, for electrical propagation within the left and right atria. The incisions direct the electrical impulse from the SA node along a specified route through all regions of both atria, causing uniform contraction required for normal atrial transport function. The incisions finally direct the impulse to the AV node to activate the ventricles, restoring normal atrioventricular synchrony. The incisions are also carefully placed to interrupt the conduction routes of the most common reentry circuits. The maze procedure has been found very effective in curing atrial fibrillation. However, not only is the maze procedure technically difficult to do, it also requires open heart surgery and is very expensive.
Maze-like procedures have also been developed utilizing electrophysiology procedures, which involve forming lesions on the endocardium (the lesions being 1 to 15 cm in length and of varying shape) using an ablation catheter to effectively create a maze for electrical conduction in a predetermined path. The formation of these lesions by soft tissue coagulation (also referred to as “ablation”) can provide the same therapeutic benefits that the complex incision patterns of the surgical maze procedure presently provides, but without invasive open heart surgery.
Frequently, an arrhythmia aberration resides at the base, or within one or more pulmonary veins, wherein the atrial tissue extends. To treat such an aberration, physicians use one or more catheters to gain access into interior regions of the pulmonary vein tissue for mapping and ablating targeted tissue areas. Placement of mapping and ablation catheters, or alternatively a combined mapping/ablation catheter, within the vasculature of the patient is typically facilitated with the aid of an introducer guide sheath and/or guide wire.
The introducer guide sheath may be introduced into the left atrium of the heart using a conventional retrograde approach, i.e., through the respective aortic and mitral valves of the heart. Alternatively, a more simple approach is to introduce the introducer guide sheath into the left atrium using a transeptal approach, i.e., through the atrial septum (i.e., fossi ovalis). A detailed description of methods for introducing an introducer guide sheath into the left atrium via a transeptal approach is disclosed in U.S. Pat. No. 5,575,810, issued to Swanson et al., which is fully and expressly incorporated herein by reference. Once the guide sheath is inside the left atrium, the catheter must be advanced through the guide sheath, into the left atrium, and then maneuvered into or adjacent to a desired pulmonary vein (typically with the aid of a guidewire) before mapping and/or ablating. The pulmonary vein may be one of the two left pulmonary veins or one of the two right pulmonary veins.
Positioning of the sheath and guidewire are critical to the success of this procedure, since they are the conduit for the ablation catheter and/or mapping catheter. However, the anatomical location of the atrial septum is closer in proximity to the right pulmonary veins than it is to the left pulmonary veins. Thus, once the guide sheath passes through the atrial septum, the right pulmonary veins are substantially immediately adjacent to the distal end of the guide sheath while the left pulmonary veins are located on substantially the opposite side of the left atrium from the distal end of the guide sheath. As a result, the guide sheath must be maneuvered differently when placing the catheter in contact with the left pulmonary veins as opposed to the right pulmonary veins. While steerable guide sheaths can be used to facilitate the introduction of the catheter within the desired pulmonary vein, the simple curves provided by such steerable guide sheaths do not easily allow the guidance of the catheter within both the left and right pulmonary veins.